JP2021113349A - Manufacturing method of target - Google Patents

Abstract

To provide a technology for depositing a NiO film with a uniform concentration of Li.SOLUTION: An aspect of the technology provides a manufacturing method of a target for depositing a NiO film containing Li. The manufacturing method of the target for depositing this NiO film containing Li includes a step where a mixed power of a powder containing LiNiO2 and a powder containing NiO is sintered at a sintering temperature lower than a melting point of LiNiO2. A mixture ratio of these powders is not limited to, but for example a ratio of 0.01 wt.% to 30 wt,% at which a powder including LiNiO2 may be mixed to a power containing NiO.SELECTED DRAWING: Figure 2

Description

The technique disclosed herein relates to a method for producing a target for forming a NiO (nickel oxide) film containing Li (lithium).

Patent Document 1 discloses a method for producing a NiO film containing Li. In this production method, a Li-containing NiO sintered body is used as a target.

Japanese Unexamined Patent Publication No. 2004-091253

Generally, in the target manufacturing method, a step of sintering the raw material at a sintering temperature of about 700 ° C. and a step of cooling after that are executed. The target used in the above-mentioned method for producing a NiO film contains Li powder as a raw material. Since the melting point of Li (about 180 ° C.) is lower than the sintering temperature, Li melts in the above-mentioned target sintering step. After that, Li solidifies in the cooling step. As a result, Li segregation may occur in the manufactured target. If Li segregation occurs in the target, a NiO film having a non-uniform Li concentration may be formed when a film is formed using the segregation of Li. The present specification provides a technique for forming a NiO film having a uniform Li concentration.

The technique disclosed herein is embodied in a method for producing a target for forming a Li-containing NiO film. This production method includes _{a step of sintering a mixed powder of a powder containing LiNiO 2} (lithium nickelate) and a powder containing NiO at a sintering temperature lower than the melting point of _{LiNiO 2.}

_{In the above-mentioned production method, LiNiO 2} powder having a relatively high melting point is used as the raw material powder containing Li. Therefore, the sintering of the mixed powder containing it can be carried out at a sintering temperature lower than the melting point of _{LiNiO 2.} As a result, LiNiO ₂ does not melt during the sintering process. Therefore, by suppressing the segregation of Li described above, it is possible to produce a target having a uniform Li concentration. Furthermore, by forming a film using the target, a NiO film having a uniform Li concentration can be formed.

The process relating to the manufacturing method of the target 10 of an Example is shown. A schematic diagram of a film forming apparatus 12 for producing a Li-containing NiO film using the target 10 of the example is shown. A schematic diagram of the film forming apparatus 60 of the reference example is shown.

A film forming method, which is an embodiment of the present technology, will be described. In this film forming method, a Li-containing NiO film is formed, _{and a sintered body of LiNiO 2} powder and NiO powder is used as the target 10 as the film forming material. Here, the LiNiO ₂ powder broadly means a powder _{mainly containing LiNiO 2} , and is not limited to a powder containing only _{LiNiO 2.} Similarly, the NiO powder broadly means a powder mainly containing NiO, and is not limited to a powder containing purely NiO alone.

First, a method for manufacturing the target 10 used in this embodiment will be described with reference to FIG. First, in step S1, the LiNiO ₂ powder and the NiO powder are mixed. This mixed powder may be hereinafter referred to as a mixed powder. The mixing ratio of the powder may be determined by the acceptor density of the NiO film obtained by the film formation using the target 10. The mixing ratio of the powder is not particularly limited, but for example, the LiNiO ₂ powder may be mixed at a ratio of 0.01 wt% to 30 wt% with respect to the NiO powder. In this example, 0.13 wt% of LiNiO ₂ powder was mixed with NiO powder to prepare a mixed powder.

Then, in step S2, the mixed powder is sintered by being pressed under predetermined conditions. The sintering temperature may be set to a general temperature such as 700 ° C. The specific value of the sintering temperature is not particularly limited, but it is preferable that the sintering temperature is lower than the melting point of _{Linio 2.} In this regard, since _{the melting point of LiNiO 2} is higher than 1000 ° C., the sintering temperature can be set to a sufficiently high temperature.

The sintered body formed in step S2 is then cooled in step S3. The cooling method is not particularly limited, but slow cooling may be performed. The target 10 of this embodiment is manufactured by the above manufacturing method.

_{In the above-mentioned production method, LiNiO 2} powder having a relatively high melting point is used as the raw material powder containing Li. Therefore, the sintering of the mixed powder containing it can be carried out at a sintering temperature lower than the melting point of _{LiNiO 2.} As a result, LiNiO ₂ does not melt during the sintering process. Therefore, by suppressing the segregation of Li, the target 10 having a uniform Li concentration can be produced.

Next, with reference to FIG. 2, a method of forming a Li-containing NiO film using the target 10 described above will be described. The film forming method using the target 10 is not particularly limited, but various sputterings such as DC sputtering and RF sputtering and PLD (Pulse Laser Deposition) can be adopted.

FIG. 2 shows a film forming apparatus 12 for producing a NiO film using the target 10 of this embodiment. The film forming apparatus 12 is an apparatus for performing high frequency sputtering by applying an RF voltage. The film forming apparatus 12 includes a vacuum chamber 14 and vacuum pumps 18 and 20. The vacuum pumps 18 and 20 include a first vacuum pump 18 and a second vacuum pump 20. The vacuum pumps 18 and 20 are arranged outside the vacuum chamber 14 and are connected to the vacuum chamber 14. The vacuum pumps 18 and 20 can reduce the pressure inside the vacuum chamber 14 and control the degree of vacuum to a predetermined degree. The types of the vacuum pumps 18 and 20 are not particularly limited, but the first vacuum pump 18 may be, for example, a cryopump for high vacuum exhaust. The second vacuum pump 20 may be, for example, a dry pump. Although two vacuum pumps are used in this embodiment, the number of vacuum pumps is not particularly limited.

The film forming apparatus 12 further includes gas supply devices 22 and 24. The gas supply devices 22 and 24 are arranged outside the vacuum chamber 14 and are connected to the vacuum chamber 14. The gas supply devices 22 and 24 can supply sputter gas to the inside of the vacuum chamber 14. The gas supply devices 22 and 24 include a first gas supply device 22 and a second gas supply device 24. The gas supply devices 22 and 24 include a supply source 25, a supply pipe 26, and a control valve 28. The gas supplied from the supply source 25 is supplied to the control valve 28 through the supply pipe 26. The control valve 28 can arbitrarily control the amount of gas supplied to the vacuum chamber 14. The gas whose flow rate is controlled by the control valve 28 is supplied to the vacuum chamber 14. The control valve 28 is not particularly limited, but may be, for example, a mass flow controller. The type and number of sputter gases supplied from the gas supply devices 22 and 24 are not particularly limited _{, but may be Ar (argon) gas or O 2} (oxygen) gas. When a plurality of sputter gases are used, the sputter gas supply ratio may be controlled to an arbitrary ratio by the control valve 28.

The film forming apparatus 12 further includes a substrate stage 16 and a cathode 32. The substrate stage 16 is arranged inside the vacuum chamber 14. On the substrate stage 16, the substrate 30 on which the NiO film is formed can be arranged. The cathode 32 is arranged inside the vacuum chamber 14 and is attached at a position facing the substrate stage 16. The target 10 can be arranged on the cathode 32. A power supply 44 is connected to the cathode 32. The cathode 32 may be, for example, a magnetron RF sputtered cathode. Further, on one surface of the target 10 arranged on the cathode 32 (that is, the back side of the surface facing the substrate 30), the horizontal magnetic field of the other surface of the target 10 (that is, the surface facing the substrate 30) is applied. The permanent magnet 40 may be provided so as to have a predetermined value.

The film forming apparatus 12 further includes a shutter 36. The shutter 36 is arranged between the substrate stage 16 and the cathode 32 facing each other. The shutter 36 is controlled to be openable and closable by the controller 42. The controller 42 is not particularly limited, but may be, for example, a rotating air cylinder.

An example of forming a Li-containing NiO film on the surface of the substrate 30 by using the film forming apparatus 12 as described above will be described. A magnetron RF sputtered cathode was used as the cathode 32. Further, on one surface of the target 10, a plurality of permanent magnets 40 are arranged so that the horizontal magnetic field of the other surface of the target 10 is 500 G.

First, the substrate 30 to be formed was placed on the substrate stage 16. The substrate 30 is not particularly limited, but is a gallium oxide substrate. Subsequently, the inside of the vacuum chamber 14 was depressurized by the vacuum pumps 18 and 20, and the internal pressure was reduced to 1 × 10 ^-5 Pa or less. Subsequently, the sputter gas was supplied to the vacuum chamber 14 by the gas supply devices 22 and 24. Ar gas and O ₂ gas were used as the sputtering gas. The sputter gas supplied to the vacuum chamber 14 was controlled by the control valve 28 so that the mixing ratio of _{Ar gas and O 2 gas was 10: 3.}

Next, 200 W of electric power was applied to the target 10. As a result, magnetron sputtering by RF was performed in the vacuum chamber 14. During the execution of magnetron sputtering, the shutter 36 was opened and closed according to a predetermined film forming condition under the control of the controller 42. As described above, a Li-containing NiO film is formed on the surface of the substrate 30 on the substrate stage 16. Each operation of the film forming apparatus 12 described above may be performed according to the operation of the operator, or may be automatically advanced by the film forming apparatus 12.

The electrical resistivity of the substrate 30 formed by the above method was 0.83 Ωcm. On the other hand, the electrical resistivity of the substrate formed under the same conditions without doping the target with Li was 7.8 Ωcm. That is, by doping the target with Li, the electrical resistivity of the substrate 30 after the film formation is lowered. Therefore, it was confirmed that Li was incorporated into the NiO film without increasing defects and functioned as a p-type carrier acceptor.

Next, the film forming apparatus 60 of the reference example will be described with reference to FIG. In the film forming apparatus 60 of this reference example, the internal configuration thereof is changed as compared with the film forming apparatus 12 of the embodiment shown in FIG. Specifically, in this reference example, a plurality of targets 62 and 64 are used. Therefore, a plurality of cathodes 66, 68 and a plurality of shutters 70, 72 are provided so as to correspond to the plurality of targets 62, 64. Since the other configurations are the same as those of the film forming apparatus 12 of the above-described embodiment, the same reference numerals are given here, and duplicate description will be omitted.

In the film forming apparatus 60 of this reference example, a plurality of targets 62 and 64 having different configurations are used. The targets 62 and 64 include a first target 62 and a second target 64. The first target 62 is composed of NiO, and more specifically, it is a sintered body of NiO powder. The second target 64 is mainly composed of LiNiO ₂ , and more specifically, it is a sintered body of _{Linio 2 powder.} That is, the second target 64 contains Li and supplies Li in the film forming process. _{As for the second target 64 of this reference example, LiNiO 2} powder having a relatively high melting point is used as the raw material powder containing Li, so that Li is used in the process of producing the powder (particularly, the step of sintering). Segregation is suppressed.

The film forming apparatus 60 includes a plurality of cathodes 66 and 68. A first target 62 is arranged on the first cathode 66. A second target 64 is arranged on the second cathode 68. Further, the respective cathodes 66 and 68 may be selected by a film forming method, and may be, for example, a magnetron RF sputtered cathode. Further, one surface of each of the cathodes 66 and 68 (that is, the back surface of the surface facing the substrate 30) has the other surface of the corresponding targets 62 and 64 (that is, the surface facing the substrate 30). Permanent magnets 40 may be provided so that the horizontal magnetic field has a predetermined magnitude.

The film forming apparatus 60 further includes a plurality of shutters 70 and 72. The plurality of shutters 70 and 72 include a first shutter 70 and a second shutter 72. The plurality of shutters 70 and 72 are arranged at positions facing the targets 62 and 64, which are opposed to each other. Each of the shutters 70 and 72 is controlled to be openable and closable by the controller 42.

Using the film forming apparatus 60 as described above, a Li-containing NiO film was formed on the surface of the substrate 30 by the following procedure. Since the procedure is the same as the film forming method using the film forming apparatus 12 of the embodiment from the first arrangement of the substrate 30 on the substrate stage 16 to the control of the sputtering gas by the control valve 28, the procedure will be described. Omit. As for the substrate 30, a gallium oxide substrate is also used.

First, 200 W of electric power was applied to the first target 62. As a result, plasma was formed in the space near the surface of the first target 62. Subsequently, 30 W of electric power was applied to the second target 64. As a result, plasma was also formed in the space near the surface of the second target 64. After that, the shutters 70 and 72 corresponding to the plurality of targets 62 and 64 were opened at the same time.

By the above procedure, the substrate 30 was formed with sputtered particles generated from each of the first target 62 and the second target 64. In this reference example, the plurality of shutters 70 and 72 are opened at the same time, but the plurality of shutters 70 and 72 may be opened alternately. In that case, the amount of evaporation from the second target 64 containing Li can be controlled by the second shutter 72. That is, the concentration of Li in the NiO film can be controlled.

The resistivity of the substrate 30 formed by the above method was 0.91 Ωcm. As described above, the resistivity of the substrate formed under the same conditions without doping the target with Li was 7.8 Ωcm. That is, by doping Li, the electrical resistivity is lowered. Therefore, it was confirmed that Li was incorporated into the NiO film without increasing defects and functioned as a p-type carrier acceptor.

Although some specific examples have been described in detail above, these are merely examples and do not limit the scope of claims. The techniques described in the claims include various modifications and modifications of the specific examples illustrated above. The technical elements described herein or in the drawings exhibit their technical usefulness alone or in combination.

10, 62, 64: Target 12, 60: Cathode 14: Vacuum chamber 16: Substrate stage 18, 20: Vacuum pump 22, 24: Gas supply device 25: Supply source 26: Supply pipe 28: Control valve 30: Substrate 32, 66, 68: Cathode 36, 70, 72: Shutter 42: Controller

Claims (1)

A method for producing a target for forming a Li-containing NiO film.
A step of sintering a mixed powder of a powder containing LiNiO ₂ and a powder containing NiO at a sintering temperature lower than the melting point of _{LiNiO 2 is provided.}
Production method.

Images